The present invention relates to wireless networks and, more particularly, to power control of a downlink shared channel in the context of downlink transmit diversity.
Universal Mobile Telecommunications System (UMTS) is to be the third generation mobile system, which is to offer higher data rates and a wide range of telecommunications services, including support for multimedia. UMTS will provide high-quality services with efficient use of network resources. UMTS is to be based on the Global System for Mobile communications (GSM) with some major modifications, e.g., a new radio interface. The UMTS network is to support both circuit-switched and packet-switched services. The circuit-switched technology will be based on the current GSM circuit-switched technology and the packet-switched technology on the General Packet Radio Service (GPRS), which is a new packet service for GSM.
The architecture of UMTS is thus to be based on GSM/GPRS. However, the access network part of UMTS will be new and revolutionary compared to GSM. The UMTS Terrestrial Radio Access (UTRA) Network (UTRAN) will be the new radio interface, which will be able to operate in two different modes: Wideband Code Division Multiple Access (WCDMA) and Time Division/Code Division Multiple Access (TD/CDMA). On the core network side, UMTS will consist of enhanced GSM-based circuit-switched and GPRS-based packet-switched core networks. UTRAN will have the ability to support multiple simultaneous connections for one user, i.e., simultaneous packet- and circuit-switched connections, and every connection can have individual properties, e.g., QoS (quality-of-service) parameters. Contrary to GPRS, UTRAN can also guarantee throughput for a packet-switched connection. This property is vital for some multi-media applications. Despite the wider bandwidth available in the UMTS system compared to GSM, the radio part of the system will remain the most susceptible to bottlenecks. As always, the design objective is an efficient use of limited resources without compromising versatility.
The UMTS packet network architecture will be highly similar to GPRS. However, the naming of some elements and interfaces has been changed from GPRS. FIG. 1 shows the GPRS network architecture, and FIG. 2 shows the UMTS packet network architecture. The UMTS packet network consists of the following network elements:
3G-SGSN: it will be the third generation version of the serving GPRS support node (SGSN).
3G-GGSN: it will be the third generation version of the gateway GPRS support node (GGSN).
HLR: it will be the GSM home location register (HLR) with some updates.
Node B: it will correspond to base transceiver station (BTS) in GSM.
RNC (Radio Network Controller): it will correspond to base station controller (BSC) in GSM.
The core network (CN) part of the packet-switched side will consist of 3G-SGSN, 3G-GGSN and HLR elements. The packet core network will include also the backbone network for connecting core network elements 3G-SGSN and 3G-GGSN together.
Node B and RNC will comprise the radio access network (RAN) part of the UMTS network. RAN will correspond to GSM""s BSS (Base Station Subsystem). The responsibility of RAN is the handling of all radio-specific functions, e.g., radio channel ciphering, power control, radio bearer connection setup and release. The basic separation between elements will be that Node B will handle the physical layer functions, and RNC will handle the management functions. However, the separation might be slightly different than in GSM.
As can be seen by comparing FIGS. 1 and 2, the biggest architectural difference will be the new interface (Iur) inside RAN. It will reside between RNCs. In this connection, UMTS introduces a new concept called macrodiversity. In a macrodiversity situation, data will be sent via multiple Node Bs. Because signals will transferred via multiple routes over the air interface and combined in the MS and RNC, e.g., the fading effect will be less harmful, and thus lower power levels can be used. However, those Node Bs may belong to the area of two or more different RNCs, so the interface, i.e., Iur-interface between RNCs is required. In this situation, as shown in FIG. 3, the RNC can be in two logical roles. the RNC can be logically either a xe2x80x9cdriftxe2x80x9d RNC (DRNC) or a xe2x80x9cservingxe2x80x9d (SRNC).
The actual termination point of the Iu-interface will be SRNC, as shown for both logical possibilities in FIG. 3. The Iu-interface will connect the radio access network (RAN) and core network (CN), whether it be packet- or circuit-switched. SRNC will control information transfer and request radio resources from appropriate DRNCs. The DRNC will only relay information between the MS and SRNC, which is depicted in FIG. 3.
Cell level mobility issues will be handled within UTRAN. When there exists a dedicated connection to the user equipment, the UTRAN will handle the radio interface mobility of the UE. This includes procedures such as soft handover.
For the new macrodiversity concept for 3G, it will be possible to set up multiple radio links simultaneously between a user equipment, for instance, a mobile station, in a wireless telecommunications system, in order to be in a position to decide which of the wireless links from a plurality of base stations is preferred at any given point in time during a communications session and to switch seamlessly between the radio links during the session depending on which link is preferred. In other words, a switch to a base station with a stronger signal can be made without having to set up a new connection. This means that the user equipment should be in a position to measure the magnitude of at least one parameter of the plural radio links simultaneously established between the user equipment and more than one of the plurality of base stations in order to periodically decide which one of the more than one of the plural radio links is currently preferred for use in the communications session between the user equipment and an end terminal connected to the system.
Thus, a soft handover is a category of handover procedures where the radio links are added and abandoned in such a manner that the user equipment (UE) always keeps at least one radio link to the UTRAN. For instance, as shown in FIG. 4, several Node B base stations (BS1, BS2, BS3) are illustrated in several corresponding cells. A user equipment in the form of a mobile station (MS) is shown moving from one cell to another. As the distance from base station 1 (BS1) increases, as illustrated in FIG. 5, the received signal strength from base station 1 at the mobile station decreases, while the received signal strength from base station 2 (BS2) increases. This is particularly noteworthy in a region of base station diversity shown as a distance window, with the signal strengths from base station 1 and base station 2 crossing over inside the window. Within a threshold region of signal strength, a soft handover can be effected, whereby the mobile station always keeps at least one radio link to the UTRAN effective. A This is distinguished from a hard handover, which would be a handover between different frequencies or between WCDMA and GSM (or a switch from FDD (Frequency Division Duplex) to TDD (Time Division Duplex) within UMTS).
It will be important for WCDMA power control to ensure that each user equipment receives and transmits just enough energy to properly convey information while interfering with other users no more than necessary. As shown in FIG. 6, several mobile stations (MS1, MS2, MS3, MS4) are shown communicating with a base station within a cell via corresponding radio links. FIG. 7 shows received power at the base station (BS) without power control, and FIG. 8 shows received power at the base station with optimal power control. In the downlink direction, a single mobile station sees the power levels of the whole transmission from the base station, and the power levels should in the ideal case vary as a function of the path loss in the downlink, and thus the power levels for optimal power control are different at the different observation points. It is proposed in UMTS to provide a group of functions to control the level of transmitted power, in order to minimize interference and keep the quality of the connections. The proposed functions consist of up and downlink outer loop power control, up and downlink inner loop power control, and up and downlink open loop power control for both ordinary and compressed transmit power.
The open loop power control for both the uplink (UL) and downlink (DL) sets the initial power of the user equipment (UE), i.e., at random access. The function uses UE measurements and broadcasts the cell/system parameters as input. The function is located both in the UTRAN and the UE. The downlink open loop power control receives downlink measurement reports from the UE.
The uplink and downlink inner loop power control set the power of the uplink and downlink dedicated physical channels. For the uplink inner loop power control in FDD, it is a closed loop process located in Node B for FDD. It receives the quality target from the uplink outer loop power control (discussed below), and quality estimates of the uplink dedicated physical control channel. The power control commands are sent on the downlink dedicated physical control channel (DPCCH) to the UE. This function is located in both the UTRAN and the UE.
The uplink outer loop power control is located in the SRNC and sets the target quality value for the UL inner loop power control (which is located in Node B for FDD). It receives input from quality estimates of the transport channel. The UL outer loop channel is used mainly for a long-term quality control of the radio channel. The target quality value is sent to the UE by the SRNC. In FDD, if the connection involves both an SRNS and a DRNS, the function of UL outer loop power control (located in the SRNC) sets the target quality for the UL inner loop power control function (located in Node B).
Similarly, the downlink inner loop power control sets the power of the downlink dedicated physical channels. It receives the quality target from the DL outer loop power control and quality estimates of the downlink dedicated physical control channel. The power control commands are sent on the uplink dedicated physical control channel to the UTRAN. This function is located in both the UTRAN and the UE. For instance, FIG. 9 shows an uplink inner loop power control for two mobile stations (MS1, MS2) in communication with a base station (BS) on corresponding uplinks (P1, P2). If the SIR (Signal-to-Interference Ratio) detected is greater than the SIR set by the UL outer loop power control, then appropriate xe2x80x9cdownxe2x80x9d TPC (transmit power control) commands are sent on the downlink. On the other hand, if the detected SIR is less than the target, the TPC commands command an up increment of power from the mobile station. Typically, the up or down command would be 1 dB within an approximately 70 dB range (21 dBm to xe2x88x9250 dBm) for the uplink and within an approximately 20 dB range for the downlink.
The power control of the downlink shared channel (DSCH), which is a transport channel shared by several UEs and associated with a dedicated channel, can also be controlled in this way (see 3G TS 25.214 v.3.1.1 (1999-12) at Sec. 5.2.2). But the UMTS specifications do not specify exactly how the DSCH power control is normally to be done. Basically, two alternatives exist. Either the DSCH is made to follow the DCH power variations, or the DSCH power level is fixed. For instance, for common channels the approach of the prior art would be to just use a fixed power level or to control the power level slowly via the RNC to follow the dedicated channel power level (although such an approach is not believed to have yet been specified in the interface specifications). As mentioned above, in the downlink direction, a single mobile station sees the power levels of the whole transmission from the base station, and the power levels should, in the ideal case, vary as a function of the path loss in the downlink, and thus the power levels for optimal power control are different, depending upon the location of the mobile station. If the power level for DSCH is fixed, then the power for all users is the same in the downlink and should be sufficient to reach a mobile station at the cell edge, although some of the users would need much less power in practice. On the other hand, if the DSCH power control is done based on the DCH power control, there will be a problem on soft handover. The reason for this is that the user equipment (UE) selects a primary cell periodically by measuring the RSCP (received signal code power) of CPICHs (common pilot channels) transmitted by the active cells. The cell with the highest CPICH RSCP is detected as a primary cell. Normally when a new base station is added, it is expected that the base station can assume that it is primary or close to the primary in the power level for that UE, especially if DSCH traffic for that terminal is handed over to that base station, but then afterwards information is not given if other base stations are dropped or added to the active set in the soft handover state. The prior art methods have no real means to determine if the signal from the base station is the strongest one the terminal is receiving.
Thus, for power control of DSCH, the problem is that the base station is not continually updated on whether the initially indicated soft handover state is still valid or not. Consequently, it could be the case that the power control of the DSCH is being done based on a non-dominating DCH. This would mean that the DSCH power level would be too low.
A solution would be to add a parallel power control loop for DSCH use. But this would be a problem, because DSCH does not contain any pilot bits, and it also has long periods of silent duration. A parallel power control loop for DSCH use, such as a 100 Hz parallel power control loop, would not necessarily be very well xe2x80x9cup-to-datexe2x80x9d when the transmission on DSCH is initiated (such a solution might, for instance, borrow n symbols per 10 millisecond frame from the existing power control command stream for DSCH use; if borrowing one symbol per 10 millisecond frame the resulting rate would be 100 Hz). Another possibility would be to add a second, fully parallel stream with separate symbols, also with a rate of 1500 Hz (15 slot frames provided at 1500 Hz rate with one slot per frame for power command) for DSCH. But this would be burdensome and would require more changes to the current specification. Also, controlling DSCH on its own is not feasible, since DSCH is discontinuous and since it does not provide reference (pilot) symbols.
An object of the present invention is to provide a power control of a downlink shared channel in the context of downlink transmit diversity.
According to a first aspect of the invention, a method for use in a wireless telecommunications system having at least one user equipment (UE) and a plurality of base stations connected to a common network controller, wherein said UE is able to periodically determine the magnitude of at least one parameter of plural radio downlinks simultaneously established from more than one of said plurality of base stations to said UE in order to periodically decide which one of said more than one of said plural radio downlinks is from a currently preferred base station for use in a communications session between said UE and an end terminal in communication with said system, comprises the steps of periodically signaling on an uplink from said UE to at least one of said more than one of said plurality of base stations that a downlink to said UE from said at least one of said more than one of said plurality of base stations is or is not from said currently preferred base station, and periodically selecting, in response to said periodic signaling on said uplink from said UE, a power control method for at least said downlink to said UE from said at least one of said more than one of said plurality of base stations.
Further in accordance with the first aspect of the invention, a method wherein in response to said signaling step signaling that said downlink to said UE from said at least one of said one or more base stations is not from said currently preferred base station, said step of periodically selecting selects a fixed power level control method for said downlink to said UE from said not currently preferred base station.
Still in accordance with the first aspect of the invention, a method wherein in response to said signaling step signaling that said downlink from said at least one of said one or more base stations to said UE is from said currently preferred base station, said step of periodically selecting selects a power control method based on a power level of another, related downlink to said UE from said currently preferred base station.
According to a second aspect of the invention, an apparatus for use in a wireless telecommunications system having at least one user equipment (UE) and a plurality of base stations connected to a common network controller, wherein said UE is able to periodically determine the magnitude of at least one parameter of plural radio downlinks simultaneously established from more than one of said plurality of base stations to said UE in order to periodically decide which one of said more than one of said plural radio downlinks is from a currently preferred base station for use in a communications session between said UE and an end terminal in communication with said system, comprises means for periodically signaling on an uplink from said UE to at least one of said more than one of said plurality of base stations that a downlink to said UE from said at least one of said more than one of said plurality of base stations is or is not from said currently preferred base station, and means for periodically selecting, in response to said periodic signaling on said uplink from said UE, a power control method for at least said downlink to said UE from and said at least one of said more than one of said plurality of base stations.
In accordance with the second aspect of the invention, an apparatus wherein said means for periodically selecting, in response to said signaling step signaling that said downlink to said UE from said at least one of said one or more base stations is not from said currently preferred base station, selects a fixed power level control method for said downlink to said UE from said not currently preferred base station.
Further in accordance with the second aspect of the invention, an apparatus wherein said means for periodically selecting, in response to said signaling step signaling that said downlink from said at least one of said one or more base stations to said UE is from said currently preferred base station, selects a power control method based on a power level of another, related downlink to said UE from said currently preferred base station.
According to a third aspect of the invention, a user equipment (UE) for use in a wireless telecommunications system having at least one said UE and a plurality of base stations connected to a common network controller, wherein said UE is able to periodically determine the magnitude of at least one parameter of plural radio downlinks simultaneously established from more than one of said plurality of base stations to said UE in order to periodically decide which one of said more than one of said plural radio downlinks is from a currently-preferred base station for use in a communications session between said UE and an end terminal in communication with said system, said UE comprises sensing means, responsive to a downlink signal from a plurality of base stations for providing a corresponding plurality of sensed signals, storage means responsive to said plurality of sensed signals for storing said plurality of sensed signals and for providing said plurality of sensed signals from storage upon demand, comparator means responsive to said plurality of sensed signals retrieved from said storage means for comparing a parameter relating to said sensed signals for providing an comparison signal indicative of a comparison between the parameter magnitudes of said sensed signals, selection means responsive to said comparison signal from said comparator means for selecting a preferred base station and for providing a selection signal indicative thereof, and signaling means responsive to said selection signal for providing an uplink signal indicative of the preferred base station.
According to a fourth aspect of the invention, an apparatus for use in a wireless telecommunications system having at least one user equipment (UE), wherein said system includes a plurality of base stations connected to a common network controller, wherein said UE is able to periodically determine the magnitude of at least one parameter of plural radio downlinks simultaneously established from more than one of said plurality of base stations to said UE in order to periodically decide which one of said more than one of said plural radio downlinks is from a currently-preferred base station for use in a communications session between said UE and an end terminal in communication with said system, wherein said apparatus is responsive to a selection signal from a user equipment indicating an identification of a preferred base station, said apparatus comprises selecting means responsive to said uplink signal for determining whether the base station is preferred or not and providing a selection signal indicative thereof, and power control means responsive to said selection signal, for providing a downlink control signal to said user equipment with a power level selected according to whether or not a preferred base station is determined.
These and other objects, features and advantages of the present invention will become more apparent in light of the detailed description of a best mode embodiment thereof, as illustrated in the accompanying drawing.